Cardiovascular implants are preferably delivered percutaneously in order to reduce patient trauma, reduce the trauma endured by the patient and significantly reduce recovery periods. Through the use of one or more catheters that are introduced through, for example, the femoral artery, tools and devices can be delivered to a desired area in the cardiovascular system to perform many number of complicated procedures that normally otherwise require an invasive surgical procedure. The percutaneous approach is particularly attractive as an alternative to performing open-heart surgery.
Valve replacement surgery provides one example of an area where percutaneous solutions are being developed. A number of diseases result in a thickening, and subsequent immobility or reduced mobility, of heart valve leaflets. Such immobility also may lead to a narrowing, or stenosis, of the passageway through the valve. The increased resistance to blood flow that a stenosed valve presents can eventually lead to heart failure and ultimately death.
In the case of an aortic valve replacement, a catheter is inserted into the femoral artery and navigated, with or without a guidewire, through the artery, around the aortic arch, and into the heart at the location of the aortic valve. The ease with which the catheter is navigated greatly increases with a reduction in catheter size. In order to reduce catheter size, however, implants having a small delivery profile are required. These implants must be able to expand to the size of the native anatomical feature, such as the aortic valve, in order to be effective.
One solution that has been developed is a prosthetic valve attached to a braided support structure. This device is shown and described in several Patents and Published Applications including U.S. Pat. No. 8,974,523, issued Mar. 10, 2015 to Thill et al., incorporated by reference herein. The braided support structure is a tubular mesh that is capable of being delivered via a very small diameter delivery catheter. The tubular mesh is formed one or more fine strands braided or woven together into an elongate tube. The strands may be fibrous, non-fibrous, multifilament, or monofilament. The strands exhibit shape memory such that the elongate tube may be formed into a desired folded shape, then stretched out into a very small diameter, elongated configuration. The small diameter, elongated configuration makes a very small diameter delivery catheter possible.
Upon deployment, the elongated tube is slowly pushed out of the delivery catheter, where it gradually regains its folded, constructed configuration. The tube conforms to the internal geometries of the target vessel. In addition, the braid effectively traps all emboli that may be released from the vessel walls.
As the tube continues to be pushed from the delivery catheter, it begins to fold in upon itself as it regains its constructed configuration. As it folds in upon itself, the forces exerted by each layer add together, making the structure incrementally stronger. Thus, varying levels of strength may be achieved without changing the elongated diameter of the device.
Using this folded tube, the valve can be attached such that the valve or other structure (such as a filter) in its elongated configuration within the delivery catheter does not reside within the elongated tube, but on deployment can be positioned in, above or below the tube.
In order to get this device to fold upon exiting the catheter, preformed folds are heat-set into the braided tube during manufacturing. These folds are then unfolded during the loading process. While in the catheter, the preformed folds are unable to re-fold due to the constraints placed on the device by the catheter.
The degree to which the device tends to assume a folded configuration upon exiting the catheter is a factor in the ease of device delivery. If the device does not fold completely upon delivery, an additional step of pulling the distal end of the device while pushing the proximal end of the device can be performed in order to effect the folding. However, it would be desirable if this added step were unnecessary.
Furthermore, heat setting the device is done to create an annealed configuration of the folds. However, it has been determined that the pic angles of the wires determine how strong the tendency is to fold. With this in mind, it would be desirable to develop a way to improve the ease with which the device may be unfolded while retaining a strong tendency to fold upon delivery.